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Biomedical subjects

H Guo

Publications and source records attributed to H Guo.

At least 235 records · Page 13Linked to original sources
PubMed1995

A group II intron RNA is a catalytic component of a DNA endonuclease involved in intron mobility.

The mobility (homing) of the yeast mitochondrial DNA group II intron al2 occurs via target DNA-primed reverse transcription at a double-strand break in the recipient DNA. Here, we show that the site-specific DNA endonuclease that makes the double-strand break is a ribonucleoprotein complex containing the al2-encoded reverse transcriptase protein and excised al2 RNA. Remarkably, the al2 RNA catalyzes cleavage of the sense strand of the recipient DNA, while the al2 protein appears to cleave the antisense strand. The RNA-catalyzed sense strand cleavage occurs via a partial reverse splicing reaction in which the protein component stabilizes the active intron structure and appears to confer preference for DNA substrates. Our results demonstrate a biologically relevant ribozyme reaction with a substrate other than RNA.

Base Sequence↗
PubMed1995

Morphological abnormalities in the hippocampus of the weaver mutant mouse.

The lamination of the hippocampus in the homozygous B6CBA weaver mouse (wv/wv) was compared with that in normal B6CBA littermates (+/+) and C57BL/6J mice using Nissl and Timm's staining. In Nissl-stained preparations, the normal littermates exhibit a compact, regular arrangement of pyramidal cells in area CA3 of the hippocampus. In contrast, in homozygous weaver mutant mice, the pyramidal cell layer of area CA3 frequently appears to be thicker than normal with an apparent increase of neuropil, as evidenced by the presence of cell-free spaces within the layer. Also, small ectopic clusters of pyramidal cells and sometimes the subdivision of the pyramidal cell layer into 2 or 3 layers were found throughout the dorsoventral extent of the hippocampus. In Timm's stained preparations of the normal mouse hippocampus, two clearly separated bundles of axons were seen emerging from the hilus: one bundle running above the pyramidal cell layer of area CA3 (i.e., the suprapyramidal mossy fiber layer, SPMFL), and the second bundle running below the pyramidal cell layer (i.e., the infrapyramidal mossy fiber layer, IPMFL). In contrast, in some homozygous weaver mice, the origin of the mossy fiber bundles is clearly different from normal; specifically, mossy fibers emerge in a diffuse fashion from the area between suprapyramidal and infrapyramidal mossy fiber layers. In other weaver mice, short, discontinuous bundles diverge from the infrapyramidal mossy fiber layer and invade the thickened pyramidal cell layer. In addition, ectopic pyramidal cells are situated below the IPMFL in area CA3. The morphological changes observed in hippocampus of weaver mutants are likely to be secondary to a more basic genetic defect.

Animals↗
PubMed1995

Group II intron mobility occurs by target DNA-primed reverse transcription.

Mobile group II introns encode reverse transcriptases and insert site specifically into intronless alleles (homing). Here, in vitro experiments show that homing of the yeast mtDNA group II intron aI2 occurs by reverse transcription at a double-strand break in the recipient DNA. A site-specific endonuclease cleaves the antisense strand of recipient DNA at position +10 of exon 3 and the sense strand at the intron insertion site. Reverse transcription of aI2-containing pre-mRNA is primed by the antisense strand cleaved in exon 3 and results in cotransfer of the intron and flanking exon sequences. Remarkably, the DNA endonuclease that initiates homing requires both the aI2 reverse transcriptase protein and aI2 RNA. Parallels in their reverse transcription mechanisms raise the possibility that mobile group II introns were ancestors of nuclear non-long terminal repeat retrotransposons and telomerases.

Base Sequence↗
PubMed1995

Action of alpha-amanitin during pyrophosphorolysis and elongation by RNA polymerase II.

Using defined elongation complexes formed on dC-tailed templates with Drosophila RNA polymerase II, we have examined elongation, pyrophosphorolysis, and DmS-II-mediated transcript cleavage and the inhibitory effect of alpha-amanitin on these processes. Analysis of pyrophosphorolysis on soluble or immobilized and templates confirmed that NTPs are liberated instead of dinucleotides that are released during DmS-II-mediated transcript cleavage. 10 microgram/ml alpha-amanitin completely inhibited DmS-II-mediated transcript cleavage but allowed extended pyrophosphorolysis and nucleotide addition to occur. alpha-Amanitin dramatically decreased the Vmax for nucleotide addition but only slightly affected the Km for nucleotides. Although the processes ae mechanistically distinct, both pyrophosphorolysis and DmS-II-mediated transcript cleavage frequently resulted in similar patterns of shortened transcript. Since polymerase molecules encounter similar kinetic barriers during both processes, it is possible that there is a common step in the reverse movement of the polymerase.

Amanitins↗
PubMed1995

Cocaine increases extraneuronal levels of aspartate and glutamate in the nucleus accumbens.

Intracerebral microdialysis was used to assess the effects of cocaine-HCl on extracellular concentrations of the excitatory amino acids aspartate and glutamate in the nucleus accumbens of awake, freely moving rats. After an initial equilibration period, cocaine (7.5, 15 or 30 mg/kg) or saline was injected i.p., and samples were collected for an additional 2 h. The highest dose of cocaine (30 mg/kg, i.p.) caused a 4-fold increase in glutamate levels and an 18-fold increase in aspartate levels over baseline. To verify that the source of the extracellular aspartate and glutamate was neuronal, additional experiments were conducted using Ca(2+)-free microdialysis buffer, and buffer containing 10 microM tetrodotoxin. Local perfusion with Ca(2+)-free buffer reduced the increase of extracellular aspartate and glutamate in rats injected with 30 mg/kg cocaine. Tetrodotoxin significantly decreased the cocaine-induced increase in excitatory amino acids, but not the behavioral response.

Analysis of Variance↗
PubMed1995

Purification and characterization of two potent heat-stable protein inhibitors of protein phosphatase 2A from bovine kidney.

Two heat-stable protein inhibitors of protein phosphatase 2A (PP2A), tentatively designated I1PP2A and I2PP2A, have been purified to apparent homogeneity from extracts of bovine kidney. The purified preparations of I1PP2A exhibited an apparent M(r) approximately 30,000 and 250,000 as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and gel permeation chromatography on Sephacryl S-300, respectively. In contrast, the purified preparations of I2PP2A exhibited an apparent M(r) approximately 20,000 and 80,000 as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and gel permeation chromatography on Sephacryl S-200, respectively. The purified preparations of I1PP2A and I2PP2A inhibited PP2A with 32P-labeled myelin basic protein, 32P-labeled histone H1, 32P-labeled pyruvate dehydrogenase complex, 32P-labeled phosphorylase, and protamine kinase as substrates. By contrast, I1PP2A and I2PP2A exhibited little effect, if any, on the activity of PP2A with 32P-labeled casein, and did not prevent the autodephosphorylation of PP2A in incubations with the autophosphorylation-activated protein kinase [Guo, H., & Damuni, Z. (1993) Proc. Natl. Acad. Sci. U.S.A. 90, 2500-2504]. The purified preparations of I1PP2A and I2PP2A had little effect, if any, on the activities of protein phosphatase 1, protein phosphatase 2B, protein phosphatase 2C, and pyruvate dehydrogenase phosphatase. With 32P-labeled MBP as a substrate, kinetic analysis according to Henderson showed that I1PP2A and I2PP2A were noncompetitive and displayed a Ki of about 30 and 25 nM, respectively. Following cleavage with Staphylococcus aureus V8 protease, I1PP2A and I2PP2A displayed distinct peptide patterns, indicating that these inhibitor proteins are the products of distinct genes. The N-terminal amino acid sequences of the purified preparations indicate that I1PP2A and I2PP2A are novel proteins.

Amino Acid Sequence↗
PubMed1995

The human tumor cell-derived collagenase stimulatory factor (renamed EMMPRIN) is a member of the immunoglobulin superfamily.

Tumor cell-derived collagenase stimulatory factor, renamed extracellular matrix metalloproteinase inducer (EMMPRIN), is a M(r) approximately 58,000 glycoprotein which is located on the outer surface of human tumor cells and which interacts with fibroblasts to stimulate expression of several matrix metalloproteinases in the fibroblasts. In this study, we have used several approaches to isolate a complementary DNA encoding EMMPRIN. Several peptide sequences obtained from the isolated M(r) 58,000 glycoprotein are found in the translated complementary DNA clone, verifying its identity. Computer database searches indicate that EMMPRIN is a member of the immunoglobulin superfamily and that the deduced amino acid sequence of EMMPRIN is identical to that recently reported for human basigin and M6 antigen, molecules of previously undetermined biological function.

Amino Acid Sequence↗
PubMed1995

Upregulation of gap junctional communication and connexin43 gene expression by carotenoids in human dermal fibroblasts but not in human keratinocytes.

Consumption of dietary carotenoids has been statistically associated with decreased risk of cancer at several anatomic sites. In a model murine system of carcinogenesis (the 10T1/2 assay), we have previously shown that carotenoids can inhibit chemically and physically induced neoplastic transformation. This action is strongly correlated with the ability of carotenoids to increase gap-junctional communication (GJC) by induction of connexin43 (Cx43) gene expression. Here we extend these studies to human foreskin-derived dermal fibroblasts and keratinocytes. In fibroblasts, beta-carotene and canthaxanthin at concentrations between 10(-5) and 3 x 10(-6) M were found to strongly enhance GJC in a dose- and time-dependent manner. This was accompanied by an increase in the number of immunofluorescent junctional plaques recognized by an anti-Cx43 antibody and by an increase in Cx43 protein level as determined by western blot analysis. No decrease in proliferation rates was detected by [H3]thymidine labeling. Human keratinocytes grown in monolayer culture did not respond to carotenoids in terms of GJC as measured by dye transfer, immunofluorescent analysis of Cx43 distribution, or Cx43 levels as measured by western blotting. Both cell types accumulated high levels of carotenoids. Because canthaxanthin, which has no known provitamin A activity in mammals, is as active in fibroblasts as is beta-carotene, the carotenoid with the highest provitamin A activity, the induction of GJC and Cx43 expression by carotenoids in human dermal fibroblasts seems unrelated to their provitamin A status. The lack of response of keratinocytes suggests differences in regulation of Cx43 expression or in carotenoid processing.

Anticarcinogenic Agents↗
PubMed1995

Protein phosphatase mRNA expression in Purkinje cells of staggerer and reeler mutant mice.

We used in situ hybridization to search for the expression of three protein phosphatase (PP) mRNAs in Purkinje cells of normal mice, and staggerer (sg/sg) and reeler (rl/rl) mutant mice, two strains with known Purkinje cell disorders. The expression of the mRNAs was comparable in the normal and rl/rl Purkinje cells, but considerably reduced in the sg/sg. We interpret this finding as indicating: (a) the staggerer mutant gene may directly affect the phosphatase component of the protein phosphorylation-dephosphorylation cycle in the sg/sg Purkinje cells; or (b) the reduced mRNA expression may be a secondary phenomenon, resulting from abnormal Purkinje cell function due to the lack of synaptic input.

Animals↗
PubMed1995

[Discourse on the establishment of rural medical course in Zouping County, Shandong province by Liang Shuming].

As early as 1930's, Mr. Liang Shuming established a sanitation hospital in the county experimental construction area of Zouping, Shandong province and designed a three-tier model for rural health care. He also explored the way of establishing the health care for rural maternity and children's school hygiene, public health care and itinerant medical care. All of these exert profound influence which is still active and feasible even today.

China↗
PubMed1995

[A new and simple method of evaluating left ventricular contractility and its application].

After making theoretical analysis, we detected the relationship among the maximal tension of ventricular contraction, left ventricular end-systolic pressure and stroke volume, and then derived a new and simple method of evaluating left ventricular contractility, the slope of the left ventricular end-systolic pressure-volume relation (Emax). Twelve mongrel male dogs were used to test this method. The results show that the value of Emax (0.60 +/- 0.16 kPa/ml) coming from this simple method is very close to that from complicated method; this method has good repetitiveness and is very sensitive to the variation of myocardial contraction. Using the method for evaluating left ventricular contraction after ischemia, we found the Emax more cogent than other hemodynamic parameters. Therefore, this method is an efficient method of evaluating left ventricular contraction.

Animals↗
PubMed1995

Effects of mebendazole, albendazole and praziquantel on alanine aminotransferase and aspartate aminotransferase of Echinococcus granulosus cyst wall harbored in mice.

Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) of Echinococcus granulosus cyst wall harbored in mice for 10-12 months was measured. The activities of the 2 enzymes were 3,430 +/- 1,370-4,160 +/- 1,790 and 1,560 +/- 840-2,890 +/- 1,470, respectively. When infected mice were treated ig with mebendazole (Meb) 25 mg.kg-1.d-1 for 7-14 d, or 50 mg.kg-1.d-1 for 7 d, the ALT activities of cyst walls of both collapsed and full cysts were inhibited significantly with average inhibition rates of about 50%. Another benzimidazole derivative, albendazole (Alb), also inhibited ALT activity of the cyst wall with an inhibition rate of 40.7%, but this was not the case in the treatment with praziquantel 500 mg.kg-1.d-1 of the infected mice for 14 d. When the infected mice were treated ig with the above mentioned drugs at the same regimens, no apparent effect on AST activities of the cyst wall was seen except for the group treated ig with Meb at a higher daily dose, the inhibition rates being 26% (collapsed cyst) and 43.9% (full cyst). The significance of the results has been discussed briefly.

Alanine Transaminase↗